1. Field of the Invention
The present invention relates to suspension systems for tractor trailer vehicles. In particular, the present invention relates to a suspension system for a terminal tractor which is adapted for maneuvering a trailer in a confined area and for use with various loads.
2. Prior Art
In a typical tractor trailer configuration, the forward end of the trailer is disconnectedly attached to the tractor. Tractor trailer designs are well known which utilize a saddle or fifth wheel on which the front part of the semi-trailer rests. The fifth wheel is usually above and is supported by the rear axle of the tractor.
If no suspension system is employed on the tractor, a very rough ride ensues, particularly over rough terrain.
It is advantageous to have a suspension system for the tractor vehicle which gives an acceptable ride when the tractor is traveling alone, with an empty semi-trailer, or with a fully loaded semi-trailer.
It is also advantageous to direct the force of the load on the fifth wheel to the rear axle and not to the frame.
One approach to this problem is shown in Renner et al. (U.S. Pat. No. 5,020,820) which utilizes a subframe pivoted to the main vehicle frame. The load on the fifth wheel is transmitted to the rear axle of the tractor through an A-frame.
In certain applications, such as with a terminal tractor, short trips are made shuttling trailers on short trips. The tractor can move the trailer without retracting the support legs. The fifth wheel must be frequently lowered and raised to attach trailers to the tractor.
Accordingly, it is a principal object and purpose of the present invention to stabilize the vehicle suspension as the axle moves up and down under various loads.
It is a principal object and purpose of the present invention to direct the entire trailer load on the fifth wheel to load cylinders and then directly to trailing arms.
It is a further object and purpose of the present invention to provide a suspension system wherein the fifth wheel remains parallel to the frame at all times during raising or lowering.